A particular gate valve sleeve is taught in U.S. Pat. No. 4,895,181. The sleeve disclosed in this patent uses a stiffening ring enclosed within the sleeve. Other arrangements for gate valve sleeves are disclosed in U.S. Pat. No. 4,257,447 (Clarkson), U.S. Pat. No. 2,873,943 (Williams), U.S. Pat. No. 3,659,822 (Nagi), U.S. Pat. No. 4,201,365 (Paptzun et al), U.S. Pat. No. 4,603,864 (Raftis), U.S. Pat. No. 4,623,122 (Gambetta), and U.S. Pat. No. 4,625,942 (Nelson).
In most cases, the gate valve includes an internal sleeve arrangement made of a rubber type material which resiliently distorts upon movement of the gate of the gate valve between the sealing member and returns to seal with a like seal member when the gate is fully withdrawn.
Gate valves are subject to widely varying operating conditions and preferably must satisfactorily operate under these widely varying conditions. For example, the gate valve could be opened and closed several times daily and, therefore, must be capable of opening and closing effectively. In other cases, the gate valve may be left in one position for a substantial period of time and then moved to a second position. The sleeve of the gate valve must be capable of responding to these changing conditions and any tendency of the material of the sleeve to maintain a particular set should be minimal. Other factors affecting the choice of the sealing material include the abrasiveness of the material being conveyed through the pipe, the temperature of the fluid, and the corrosiveness of the fluid.
In the past, there has been a tendency to find an elastomeric material or composite material which effectively addresses the widely varying characteristics for the sealing sleeve. In the case of U.S. Pat. No. 4,895,181, the rigidity adjacent the sealing end of the sleeve was improved by embedding directly therein a stiffening ring. Unfortunately, the widely varying operating conditions in combination with the material to be carried renders the choice of material for the sealing sleeve very difficult. There remains a need to provide a simple sealing sleeve arrangement which is capable of operating under widely varying conditions.